The invention relates to techniques for maintaining an IP (Internet protocol) connection in a mobile network.
In a packet-switched mobile network, a mobile terminal is not normally assigned a dedicated circuit-switched connection. Instead, the network establishes and maintains a session for the terminal, and data packets are sent when necessary. In order to integrate mobile terminals with office applications, it is becoming increasingly popular to maintain Internet Protocol (IP) connections over packet data channels in packet-switched mobile networks. Maintaining an IP connection to/from a mobile terminal is desirable in order to keep data banks synchronized between the mobile terminal and an office computer, for example.
Maintaining an IP connection in packet-switched mobile networks involves certain problems. For example, it consumes the mobile terminal's battery. Further, many networks apply operator-defined policies to break connections after a certain period of inactivity. This period can be quite short, such as five minutes. When the IP connection to/from the mobile terminal is disconnected, database synchronization is impossible before connection reestablishment. Connection re-establishment must be initiated from the mobile terminal's side, the network cannot initiate connection re-establishment.
But connection re-establishment involves further expenses in tariff and/or battery consumption. Yet further, since the network cannot initiate reestablishment of the IP connection, network-initiated data synchronization must be initiated by means of an out-band trigger, ie, signalling independent from the Internet Protocol. A short message service (SMS) and its derivatives are examples of theoretically suitable out-band triggering mechanisms. But a single GSM-compliant short message can only transfer approximately 160 characters, which means that it is impracticable to transfer actual data in the trigger message. This has the consequence that the subscriber must bear the expenses and delays in re-establishing the IP connection.
The mobile terminal can send keep-alive messages in order to prevent the network from disconnecting a temporarily inactive IP connection. A keep-alive message is a message sent for the purpose of preventing the network from disconnecting the IP connection.
The mobile terminal's operating parameters in respect of the keep-alive messages could be optimized for a single network, but connection break-up habits vary between networks and in a single network they may depend on roaming arrangements between operators.